228 Proceedings of the Royal Irish Academy, 



cation of the presence of arsenic. I have also ascertained that this 

 method of detecting arsenic is not alone dii-ectly applicable to where 

 it exists as arsenions acid, biit likewise to several other compounds of 

 arsenic, whether they are soluble or insoluble in water — thus, for ex- 

 ample, the two sulphides of arsenic (orpiment and realgar), the alkaline 

 arseniates, and even metallic arsenic itself if reduced to powder, will 

 readily show their arsenical nature by this test ; and we may in a few 

 moments detect by it the occurrence of arsenic in different green, 

 yellow, and orange pigments, which are still much employed in the 

 manufacture of wall papers, in painting, and in the colouring of cer- 

 tain textile, and other articles used in dress or for ornamentation. 

 Thus, for example, if a little of the colouring matter of any arsenical 

 pigment be scraped off from a wall paper, or a small piece of the paper 

 itself be taken and placed in a test-glass with a little water, and hav- 

 ing being stirred or shaken to detach the colour, a piece of the amalgam 

 be added, it will, by the blackening of the silver salt employed as 

 before described, soon indicate the presence of arsenic. In the same 

 way it can be easily demonstrated that the colouiing matter in certain 

 green tarletans, calicoes, and other articles used for dress or for orna- 

 ment, are arsenical. I may fmiher state that the presence of organic 

 matter seems to interfere but little with this test, for I have found 

 that very minute quantities of arsenious acid, when mixed with con- 

 siderable amounts of milk, tea, coffee, ale, porter, soup, or stirabout, 

 could, with almost the same facility, be detected by this method, as 

 where they were only simply dissolved in water ; thus showing that 

 the cases to which it is applicable are very extended. 



Eut I should here observe that, as in the case of Marsh's original 

 method, there is one other metal which, under certain circumstances, 

 will produce with the sodium amalgam results closely resembling 

 those occasioned by arsenic ; the metal I refer to is antimony, which is 

 capable of uniting with nascent hydrogen to form a gas (antimoniui'etted 

 hydrogen), wliich, coming in contact with nitrate of silver, produces a 

 black antimonide of that metal, by tfie following reaction : H, Sb + 3 

 Ag KO3 = Ags Sb + 3 HjSrOj, and the blackening of the silver salt 

 from the formation of that compound might be easily mistaken for the 

 effect produced by the arsenical gas. 



But owing to the fact, first pointed out by!Fleitmann,that antimoniu- 

 retted hydrogen is not evolved (except, perhaps, as a mere trace), from 

 strongly alkaline solutions, though the conditions may exist there for its 

 formation , and as the action of the sodium amalgam is to render the mixture 

 quickly alkaline, there will be only a very minute quantity of the an- 

 timony that may be present so evolved ; and, by previously rendering 

 the mixtiu-e strongly alkaline, we may almost altogether prevent the 

 evolution of that gas. If, however, we make the mixture containing 

 the antimony in solution first strongly acid, and then add the amalgam, 

 or even acidify after its addition, the antimoniui'etted hydi'ogen will 

 be evolved in abundance, producing a deep black stain on the paper 

 moistened with the nitrate of silver ; and, for the purpose of this acidi- 



